This invention relates to a method of manufacturing a MOS type semiconductor device capable of forming an active region having a small parasitic junction capacitance formed between the source or drain region and the channel stopper, and capable of forming contacts to the source and drain regions by self aligning method and making flat the surface of the semiconductor device.
In recent years, a selective oxidation process has been widely used for manufacturing semiconductor devices.
At first, a typical prior art method of manufacturing a MOS type semiconductor device will be described with reference to FIGS. 1a through 1e. As shown in FIG. 1a, a heat oxidized film 2 and a nitride film 3 are formed on a silicon substrate 1.
Then as shown in FIG. 1b, the nitride film 3 is selectively etched to form a nitride film pattern 4. At this time, channel stop layers 81 and 82 are formed by ion injection at portions other than the nitride film pattern 4 so as to prevent the generation of inversion layer under a thick field oxide region.
Then the assembly is subjected to heat oxidation to form a thick field oxide film 5 on portions outside of the nitride film mask 4 as shown in FIG. 1c. When the nitride film is used as an oxidation resistant mask, bird's beak regions invade under it to lift the opposite ends 83 and 84 thereof.
By removing the nitride film, a structure as shown in FIG. 1d is obtained in which a portion 6 becomes an active region. Thereafter predetermined well known steps are performed to obtain the fundamental structure of a MOS type semiconductor device as shown in FIG. 1e.
In FIG. 1e, 11, 12 and 13 represent aluminum electrodes for wiring, 7 and 8 diffused layers being of a conductivity type opposite to that of the silicon substrate, 10 a gate insulating film, 9 a polycrystalline silicon gate electrode, and 14 an interlayer insulating film.
Although above-described prior art method of manufacturing a MOS type semiconductor device is a very simple method, it has the following defects.
(1) Since bird's beaks are formed at the ends of the oxidized film 5, miniaturization of the device is difficult.
(2) After forming the channel stop layers a number of high temperature (about 1000.degree. C.) heat treating steps such as heat oxidation are required so that the channel stop layers 81 and 12 are deepened to increase the junction capacitance between the channel stop layer and source and drain regions, thus causing delay of the operating speed.
(3) Since the openings through a thick insulating film have sharp sloped walls, the aluminum electrodes 11 and 13 to source and drain regions tend to break.
Accordingly, it is necessary to form sufficiently large openings enough to facilitate mask alignment at the time of the contact photolithographic step and to ensure a sufficient margin for the electroconductive diffused layer, thus making it difficult to miniaturize the semiconductor device.
For the reasons described above, with the prior art method of manufacturing it has been extremely difficult to miniaturize the MOS type semiconductor device.